Ulrich P. Strauss

Thermodynamics of hydrophobic polyacids.

The thermodynamics of deprotonating hydrolyzed 1-1 copolymers of maleic anhydride with pentyl, hexyl and octyl vinyl ether was investigated by calorimetric and potentiometric methods. These polyacids undergo a transition from a compact to a random coil conformation upon ionization in aqueous media. The results were compared with those obtained previously for similar copolymers with smaller alkyl side-chains. The contributions of the enthalpy and entropy to the free energy were analyzed. The major effects appeared to be related to the charging of the compact form of the polyacids, the electrostriction of water by the completely ionized dicarboxylate groups and the reorganization of water around newly exposed alkyl side-chains arising from the conformational transition.

A comparison of the solubilization of several paraffin hydrocarbons by a polysoap

Abstract The solubilization of several paraffin hydrocarbons by a polysoap, prepared by the partial quaternization of poly-2-vinylpyridine with n -dodecyl bromide, was studied viscosimetrically in order to determine the influence of chain length and branching of the hydrocarbons. Isooctane was solubilized to practically the same extent as n -octane, indicating that chain branching is of minor consequence. However, the solubility of the hydrocarbons decreased with increasing number of carbon atoms, though not as rapidly as with ordinary soaps. The solubility of hexadecane was still 40% that of hexane. While a temperature increase speeded up the solubilization process, it did not affect the hydrocarbon solubility, and it caused only a very minor decrease in the reduced viscosity of the polysoap solutions, both in the absence and in the presence of solubilized hydrocarbon.

Short-Range Interactions Between Polyions and Small Ions

Specific short-range interactions between polyions and small ions are gradually becoming recognized for their significant and universal role in the behavior of aqueous polyelectrolyte solutions. These interactions, which are observable even with strong polyelectrolytes, — such as the alkali metal salts of polyacids — characteristically involve changes in the solvation states of the participating species and lead to deviations of the net interionic forces from Coulomb’s law. Besides being of intrinsic theoretical interest specific interactions are frequently crucial to the functioning of polyelectrolytes in technological and natural processes [1].

Microdomains in Hydrophobic Polyacids

The alternating copolymers of maleic acid and n-alkyl vinyl ethers constitute a versatile group of polyacids which are ideally suited for studying the opposing effects of hydrophobic and ionic interactions in macromolecular behavior. The members with intermediate alkyl group size (n = 4–8) have been of special interest because they undergo conformational transitions from compact to random coil structures upon neutralization by base. The compact conformation is stabilized by the hydrophobic forces between the alkyl groups which form micelle—like microdomains inside the macromolecules. A number of selected studies which have been carried out in our laboratory to characterize the hydrophobic microdomains and the conformational transitions are reviewed here. These studies include fluorescence spectroscopy of dansylated copolymers, viscosity and phase separation investigations, and potentiometric titrations. Two recently developed methods for extracting novel information from the latter are included. One involves the resolution of appropriately chosen subunits into species differing in their states of deprotonation, which for the butyl copolymer leads to bimodal population distributions in the pH range where this copolymer undergoes its conformational transition. The other involves the determination of the micelle size for the case where the polyacid is large compared to the micelle and, therefore, may contain many micelles.